x₁ = - 1
x₂ = 2
2²ˣ⁺¹ - 9ₓ2ˣ + 4 = 0
2²ˣₓ2 - 9ₓ2ˣ + 4 = 0
2ˣ = n
2n² - 9n + 4 = 0
2n² - n - 8n + 4 = 0
n(2n - 1) - 4(2n - 1) = 0
(2n - 1)(n -4) = 0
2n - 1 = 0 => n₁ = 1/2
n - 4 = 0 => n₂ = 4
2ˣ = 1/2 => 2ˣ = 2⁻¹ => x₁ = - 1
2ˣ = 4 => 2ˣ = 2² => x₂ = 2
